Tapping blast furnaces and the like



1951 B. 5. OLD

TAPPING BLAST FURNACES AND THE LIKE 3 Sheets-Sheet 1 Filed 001:. 1. 1947 4 T Um m Invenibr:

7, 1951 5. OLD 2,56%131 TAPPING BLAST FURNACES AND THE LIKE I Filed Oct. 1, 1947 I5 Shasta-62mm 2 B. 5. OLD fi fl TAPPING BLAST FURNACES AND THE LIKE 3 Sheets-Sheet 3 FiledOct. 1, 1947 Fig.

JNVENTO BRUCE SC QTT OLD BY ENT Patented Aug. 7, 195E TAPPING BLAST FURNACES AND THE Bruce Scott Old, Concord, Mass., assignor, by mesne assignments,toE.I.du Pont de Ncmonrs & Company, Wilmington, Del., a corporation of Delaware Application October 1, 1947, Serial No. 777,275

13 Claims. 1

This invention relates to the tapping of blast furnaces and the like by means and method employing an explosive charge.

In the operation of blast furnaces, as well as open hearth furnaces and other apparatusinwhich molten iron or other molten metal is drawn oif as a product, it is customary to plug the iron (or other metal) notch or tap hole with fire clay, in order to prevent outflow of the molten metal during operation. The furnace is tapped by first drilling a hole through the .fire claywhich has become hardened by the heat of the peration-- to the crust of frozen metal which overlies the inner end of the fire clay. This crust must then be penetrated, which is ordinarily done by burning through it with an oxygen flame.

This operation is time-consuming and expensive. It is also potentially dangerous to the operators engaged in it, as the molten metal within the furnace may pour so rapidly through the breach in the crust that the operators have insufficient time to reach a place of safety. The crust may vary greatly in thickness from one cast to another, and hence may at times be penetrated with unexpected rapidity. Injuries and even fatalities to the operators have occurred from the tapping operation as a result of a too-sudden rush of molten metal through the breach.

Many suggestions and efforts have been made to solve this problem, without success, prior to the present invention. In accordance with this invention, the radically new proposal has been made that the tap hole should be blasted out, and the further suggestion which has made this proposal practical in actual operation has been that this blasting should be carried out in such a way that the blast should be focused and projected against the frozen crust, and through it, thus avoiding injury to the walls of the furnace adjacent the tap hole.

For carrying out the aforesaid purposes of the present invention, a specially shaped explosive charge is used, which provides a unidirectional blast for penetrating the frozen crust while requiring a minimum of special equipment. By following the procedure of this invention, hazards to the operators due to a sudden rush of molten metal are largely or wholly eliminated, as the operators have time, after placing the charge, to move to a place of safety before firing the charge.

The shaped charge of this invention consists of a detonating explosive in such a form that it presents a hollowed-out surface (e. g. conical or hemispherical) on one side or end, which side charge, etc.

is projected forward in a pencil-like jet of very high velocity and penetrating power. This jet has, in fact, such penetrating effect that when using the more efficient types of explosive and the more effective shapes of hollowed-out surface, as little as oz. of explosive can penetrate about 5 inches of armor plate. For maximum effect, the charge should have a stand-off distance of about 2 to 4 charge diameters from the adjacent face of the body to be penetrated.

The explosive used is a detonating explosive, i. e., it has a decomposition velocity of over 1,000 meters per second and preferably much higher. Suitable explosives include TNT, pentaerythritol tetranitrate, and nitroguanidine, and mixtures of these with each other or with other detonating explosives.

As the crust to be penetrated, although solid, is at a relatively high temperature, care should be taken to avoid premature explosion of the charge due to the heat at and near the crust. Such premature explosion may be avoided either by detoi nating the charge quickly before the said heat sets it off prematurely, or by other appropriate means such as providing heat-insulation means between the charge and the crust. The latter means may include a layer of unbored fire clay, or a wad of mineral wool or other insulation which has been rammed into the hole bored into the fire clay, or insulation covering the end of the Insulation may also be provided around the charge as well as at the end thereof.

This inventioncwill now be discussed in'more detail with reference to the accompanyin drawings, which are intended merely as illustrative of preferred procedure for carrying out the invention, and not as limiting it. In the drawings:

Fig. 1 shows a sectional elevation of a portion of a furnace at and adjacent the metal notch, and with the charge in place;

Fig. 2 shows a sectional elevation of a portion of Fig. 1 adjacent the charge, and on a larger scale;

Figs. 3 and 4 show, in sectional elevation, modifications of Fig. 2; and

Figs. 5 and 6 are views corresponding to Figs. 2 and 3 showing the inclusion of a liner.

Referring now to Fig. 1, there is shown outside wall I of a furnace such as a blast furnace, with firebrick lining l2, and provided with iron (or 20 which latter is a product of the furnace op-.

erations. To tap the furnace, in accordance with this in vention, hole 22 is drilled in any usual manner through the fire clay to the frozen trust, or at least close enough thereto to permit placing of the shaped charge at a proper distance from the crust. The debris of drilling is then removed from the hole, as by an air blast. The shaped charge 23 is then introduced, as on the end of a poker rod 24, and placed with its hollowed side or end 25 toward the frozen crust. A detonator 26 is located at the other end of the charge, and is arranged to be ignited by conventional means, e. g., electrically by means of lead wires (not shown) extending back andout through the hole 22 to a suitable safe place. Poker rod 24 is then removed, and the charge is detonated. There is thus produced an intense pencil-like jet which readily penetrates the frozen crust ii. The molten metal 20 then runs out through the resultin hole, rapidly enlarging it by melting or scouring away more or less of the crust Ill and the plug I.

As already pointed out, the shaped charge may be prematurely set off by too high a temperature applied for too long a time. If the temperature adjacent the crust I8 is too high to allow a suitable length of time for placing the charge and then letting the operators go to a place of safety, heat insulation means may be interposed between the crust I8 and the charge 23, and around the charge, as already indicated. Various ways of doing this are shown in Figs. 2 and 3. In Fig. 2,-a wad of insulation 28, such as mineral wool, is inserted into the hole 22 after the debris has been blown out and before inserting the charge 23 (which is encased in a protecting and containing sheath 33 of Bakelite or other suitable material). Alternatively, such insulation may be a part of the shaped charge assembly, and be introduced therewith; and it may extend along the sides thereof. The thickness of the insulation 23 should be sufficient to keep the charge 23 at a safe temperature, but not so thick as to hold the charge at too great a distance from crust I! for effective penetration thereof. When the charge is then detonated, the jet coming therefrom readily penetrates the insulation 23 as well as crust l3, and the molten metal 20 then flows out as already described.

In the modification shown in Fig. 3, the shaped charge 23, encased in sheath 30, is placed in a close-fitting container 32 made of insulating material such as asbestos, and then inserted into hole 22. Charge 23 is first inserted into container 32 through opening 3|, and is positioned therein by sheath 30 which extends beyond the hollowed end 25 so that the charge may be at a proper stand-off distance from the crust l8. The insulating container 32 protects the charge 23 from heat both from the front and from the sides, so that the operators will have sufllcient time to leave to a place of safety after inserting the charge in hole 22. The dead air space 36 not only provides additional insulation, but serves primarily to provide (with the end wall of container 32) the preferred stand-off distance, from crust ll, of about two to four times the diameter of charge 23.

With a charge of sufficient penetrating power,

'it is not necessary to drill all the way through the hardened fire clay plug ii to crust l8. and the hole 22 may therefore be drilled into the plug Ii only as far as required in view of the pen;- trating power of the charge. This is illustrated in Fig. 4. wherein hole 22 is drilled only part way into plug I6, leaving a considerable thickness of the plug between hole 22 and crust l3. Charge 23 is encased in sheath 3. which. as indicated in Fig. 3, extends beyond the hollowed end 25 of the charge, to maintain the preferred stand-of! distance, of about two to four times the diameter of the charge, from the adjacent face 38 of the body (plug l6 and crust l8) to be penetrated. If desired, a thin metal liner 43, e. g. of steel or copper, may be provided, fitting against the hollowed face 25 of the charge. Such a liner may likewise be provided for the charge in other positions and arrangements, such as those shown in Figs. 2 and 3, as indicated at 43 in Figs. 5 and 6. g

The arrangement of Fig. 4 has the further advantage of generally requiring no special insulation means for the charge, as the latter may be far enough away from the crust I! that the temperature surrounding the charge will not set it of! prematurely. However, if desired, insulation means such as container 32 of 3 may readily be employed.

I claim:

1. Method of tapping a highly heated furnace containing normally solid metal fused to a fluid state at the high temperatures of the furnace, comprising boring into the tap hole of the furnace, insulating the bore thus formed to retard heat transfer from the furnace to the interior of the bore, mounting an explosive charge in said heat insulated bore, providing a hollowing of the inner end of said charge disposed toward the interior of the furnace so that detonation of the charge produces an explosive jet directed axially of the bore, and detonating said charge whereby to interconnect the bore with the molten content of the furnace and effect tapping thereof.

2. The method of tapping a furnace containing molten metal which includes the steps of introducing into the tap hole of the furnace a charge of a detonating explosive provided with a hollowed face which is disposed toward the interior of the furnace, interposing between the explosive charge and the walls of the tap hole laterally surrounding the charge a medium which retards the heating of the charge by the hot surrounding walls of the tape hole, introducing a further heat insulating medium between the hollowed face of the charge and the inner end of the tap hole, and detonating said charge whereby to interconnect the tap hole with the molten content of the furnace and effect tapping thereof.

3. The method of tapping a furnace containing molten metal which includes the steps of introducing into the tap hole of the furnace a charge of a detonating explosive provided with a hollowed face which is disposed toward the interior of the furnace. interposing between the explosive charge and the walls of the tap hole surrounding the charge a medium which retards the heating of the charge laterally by the hot surrounding walls of the tap hole, confining between the hollowed face and the end of the tap hole a dead air space for further retarding heating of the hollowed face, and detonating said charge whereby to interconnect the tap hole with the molten content of the furnace and effect tapping thereof.

4. The method of tapping a highly heated furnace containing normally solid metal fused to a fluid state at the high temperatures of the furnace which includes the steps of introducing to the tap hole of the furnace a charge of a detonating explosive, providing a hollowing of the inner end of the charge disposed toward the interior of the furnace to enhance penetration into the u furnace in a jet axially of the tap hole, confining between the inner end of the charge and the inner end of the tap hole a dead air space adapted to retard heating of the inner end of the charge, detonating the charge from a location remote from the tap hole and directing the jet of the charge along the tap hole toward the molten metal thereby tapping the furnace by explosively effecting penetration of the end of the tap hole.

5. The method as defined in claim 4 wherein the dead air space is filled with fibrous heat insulating material.

6. The method of tapping a furnace containing molten metal which comprises boring into the tap hole of the furnace, introducing into the bore thus formed a charge of a detonating explosive, providing a hollowing of the inner end of said charge disposed toward the interior of the furnace so that detonation of the charge produces an explosive jet directed axially of the bore, providing heat insulation between the charge and the side walls of the bore and providing further heat insulation between the inner end of the charge and the inner end of the bore to retard heat transfer from the furnace to the charge, and detonating the charge from a, location remote from the tap hole thereby tapping the furnace by explosively effecting penetration of the end of the tap hole.

7. An explosive unit adapted to be inserted in the tap hole of a metallurgical furnace for tapping the furnace, consisting of a charge of explosive, electrical detonating means to permit the charge to be detonated from a distance, heat insulation annularly surrounding the charge to preserve the charge against disintegration under the heat of the furnace until the charge can be detonated, the said heat insulation comprising a thick, porous, fibrous mass interposed between the charge and the hot surrounding surfaces of the tap hole, the said fibrous mass being of a substantially flame-resistant material, a hollowed face formed in the forward end of the charge having a generally conical surface to direct the explosion axially of the tap hole while minimizing damage to the furnace wall, and a dead air space disposed forwardly of the hollowed face and shielded by said porous, fibrous heat insulation mass as a further protection against heat transfer to the hollowed forward face.

8. An explosive unit adapted for the tapping of furnaces containing molten metal, comprising an explosive charge with a hollowed forward face, a detonator, a heat insulation covering comprising a heat retarding material surrounding the sides of the charge and projecting a substantial distance forwardly of the hollowed face to present a lateral wall of heat insulating material confining laterally a dead air space disposed forwardly of the hollowed face of the charge, and a closure for the forward end of the wall, confining th' dead air space longitudinally, the dead air space thus confined affording further heat insulation forwardly of the hollowed face.

9. An explosive unit adapted for the tapping of furnaces containing molten metal as defined in claim 8 having further a hollowed liner coving said hollowed forward face.

10. An explosive unit adapted for the tapping of furnaces containing molten metal, comprising an explosive charge with a hollowed forward face, a hollowed metal liner covering said face, a detonator, a heat insulation covering comprising a heat retarding material surrounding the sides of the charge, a dead air space disposed forward1y of the hollowed face of the charge, a. wall for confining the dead air space laterally consisting of heat insulation material formed as an extension of said covering, and a closure of heat insulation material for the forward end of said extension, confining the dead air space longitudinally.

11. An explosive unit adapted for the tapping of furnaces containing molten metal, comprising an explosive charge with a hollowed forward face, a hollowed liner covering said face, a detonator, a heat insulation covering comprising a, heat retarding material surrounding the sides of the charge and laterally extending beyond the detonator, a dead air space disposed forwardly of the hollowed face of the charge, and a wall for I confining the dead air space laterally and longitudinaly consisting of heat insulation material formed as an extension of said covering.

12. An explosive unit adapted to be inserted in the tap hole of a metallurgical furnace for breaking through the end wall of said tap hole and thereby tapping the furnace, consisting of a charge of explosive, a detonator, and heat insulating means adjacent to the charge to preserve the charge against disintegration under the heat of the furnace until the charge can be detonated, said charge having a hollowed face formed in its forward end to oppose the end wall of the tap hole and direct the explosion toward the inner end of said tap hole While minimizing damage to the furnace wall, and said heat insulating means laterally surrounding the charge and being disposed forwardly of said hollowed face to shield said face from said end wall of the tap hole.

13. An explosive unit adapted to be inserted in the tap hole of a metallurgical furnace for breaking through the end wall of said tap hole and thereby tapping the furnace, consisting of a charge of explosive, a detonator, a, body of heat insulating material laterally surrounding the charge to preserve the charge against disintegration under the heat of the furnace until the charge can be detonated, said charge having a hollowed face formed in its forward end to oppose the end wall of the tap hole and direct the explosion toward the inner end of said tap hole while minimizing damage to the furnace wall, and a hollowed liner covering said hollowed face, and said heat insulating body being disposed in part forwardly of said hollowed face to shield said face from said end wall of the tap hole.

BRUCE SCO'I'I OLD.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS OTHER REFERENCES Popular Science, February 1945, pages 66 and 67.

The Explosives Engineer, July-August 1945, pa es -163. 

